The present invention relates to apparatus for the application of a foamed treating medium to a workpiece.
An apparatus of this general type is disclosed in German Printed Application OS No. 2,523,062. This Application discloses a method and an apparatus for the uniform application of liquid treating media to textile workpieces, and it further discloses that the treating media are foamed before application.
Applicant himself has already suggested in prior applications that such foamed treating medium be applied to the workpiece not directly, but rather through a printing screen or a screen-like intermediate carrier in order to ensure a more uniform distribution of the printing medium over the surface of the workpiece. The foamed printing medium is applied to the printing screen or screen-like carrier (as used herein, the word "screen" will designate any screen-like carrier) at atmospheric pressure and can be pressed and/or aspirated through the screen.
The application of foamed printing medium to such a screen presents problems in that the screen has opened and closed surface portions, depending upon which of its many holes are blocked in order to produce a printed pattern. Considering the width of the workpiece, this means that there are regions where there is a strong demand for treating medium (i.e. regions where the holes of the screen are unblocked) and others in which there is little or no demand for treating medium. To be taken into account in this context is the fact that the foam bubbles will burst on the upper surface of the screen, so that their liquid is released to form a film on the upper surface of the screen. Particularly in the treatment of textiles with such media, it is expected that the amount of treating liquid applied per unit surface area may deviate at most by 1 to 5% from the intended quantity. This is normally achieved by applying foamed treating medium to a workpiece through a screen, but the quality of the treated workpiece is adversely affected if there are areas of the screen on which the foam ages and for example its color changes. The aged foam will, when it bubbles finally burst, release less liquid than newly supplied foam. Therefore it is necessary to ensure that the foam is constantly being used up.